The present invention relates to an EL sheet employed as a back light in an operating section of various electronic apparatuses, and to a switch employing the EL sheet.
Electronic apparatuses, as being diversified recently, includes a switch-key to be identified and operable even in a dark place. The switch-key includes a back light disposed at a rear part of an operating section. Many of the back lights employ EL sheets. A switch including the conventional EL sheet discussed above will be described hereinafter with reference to FIG. 7, in which dimensions in a thickness direction are enlarged for better understanding.
FIG. 7 shows a lateral sectional view of the switch employing an EL sheet. Light-transmissible insulating film 1 made of, e.g., polyethylene terephtalate has domed diaphragm 2, which swells upward, formed at a given place. Beneath the entire lower face of film 1, light-transmissible electrode layer 3A, made of tin indium oxide, is formed by a spattering or an electron beam method.
Luminous layer 3B, dielectric layer 3C, back electrode layer 3D, and insulating layer 3E are laid one after another beneath layer 3A by printing beneath layer 3A except bent section 2A around the root of diaphragm 2, so that EL element layer 3, as a whole, may be constructed. Luminance layer 3B includes high dielectric resin, made of fluoro rubber or cyano-system resin in which zinc sulfide, which is a base material for light emission, is dispersed. Dielectric layer 3C includes high dielectric resin in which barium titante is dispersed. Back electrode layer 3D is made of silver or carbon resin system. Insulating layer 3E is made of epoxy resin or polyester resin.
Beneath EL element layer 3, formed on the lower face of diaphragm 2, a movable contact 4 is printed, so that EL sheet 5, as a whole, may be constructed. Movable contact 4 is made of epoxy resin or polyester resin in which conductive particles such as silver or carbon are dispersed.
Circuit board 6 made of an insulating film such as polyethylene terephtalate is disposed under EL sheet 5, and a pair of fixed contacts 6Axe2x80x94facing movable contact 4 with a given clearancexe2x80x94are disposed on the upper face of board 6. Plural wiring patterns (not shown) are coupled to fixed contacts 6, so that a switch as a whole may be constructed.
Beneath insulating film 1, having an entire lower face covered with light-transmissible electrode layer 3A, EL element layer 3, which includes luminous layer 3B, dielectric layer 3C, back electrode layer 3D and insulating layer 3E, is printed. Movable contact 4 is also printed on the top of that. Then diaphragm 2 is formed using a mold, so that EL sheet 5 may be completed. EL sheet 5 is bonded to circuit board 6 with adhesive or by thermal bonding so that the switch may be completed.
The switch is mounted to an operating section of an electronic apparatus, and an alternating current (AC) voltage from a circuit of the apparatus is applied between light-transmissible electrode layer 3A and back electrode layer 3D of EL sheet 5, so that luminous layer 3B may emit light. The light illuminates the operating section of the apparatus from the back of the operating section, and thus a user can identify and operate the operating section easily even in a dark place.
Diaphragm 2 is depressed from above the diaphragm through, e.g., a key-button, then diaphragm 2 is bowed on a fulcrum, i.e., bent section 2A or its vicinity with a click feel, and thereby, movable contact 4 moves downward to contact with fixed contacts 6A. Movable contact 4 thus contacts electrically with fixed contacts 6A. When the depression is released, diaphragm 2 is restored to the status shown in FIG. 7 by resilient restoring force of the diaphragm.
The conventional EL sheet in the switch includes light-transmissible electrode layer 3A made of metallic hard film formed beneath the entire face of insulating film 1. This structure degrades the click feel and the flexibility of diaphragm 2 during operation. Thus, light-transmissible electrode layer 3A may crack when diaphragm 2 is formed or depressed repeatedly. Further, the depressing force through diaphragm 2 tends to change.
An EL sheet generates a stable click feel during an operation and is easy to be processed. A switch employs the EL sheet. The EL sheet includes the following elements:
(a) a light-transmissible insulating film having a domed diaphragm swelling upward;
(b) an EL element layer including a light-transmissible electrode layer, a luminous layer, a dielectric layer, and a back electrode layer laminated beneath the insulating film in this order except at a bent section and its vicinity around the root of the diaphragm;
(c) a first conductive pattern coupled to the light-transmissible electrode layer and formed beneath the insulating film; and
(d) a second conductive pattern being coupled to the back electrode layer and formed beneath the insulating film.
The switch includes the EL sheet and contacts being disposed under the diaphragm to resiliently and electrically contact each other.